In preparation for including `node` in the workspace run the formatter
on `node`.

rustdoc expects to be on an item. Make the docs on `tmpdir` conform to
rustdoc format.

The `getbalances` RPC method is currently being feature guarded on
`not(download)`. I'm not sure why but it seems unnecessary.

Currently we have a job for each supported version of Bitcoin Core and
in it we run the integration tests.

Note also that `node` is currently not a member of the workspace. So it
misses out on all the benefits of `run_task` (e.g., linting).

However `node` cannot be directly run using `run_task` because of its
unusual features - it requires a version feature to build.

Add a script to lint and one to run tests then call these from CI.

While we are at it update the justfile now that `node` can be linted and
formatted as part of workspace commands. Also update the
`update-lock-files` script.

Add a brief readme file, point at `cargo run -- --help` and also at the
docs we already wrote in `types/README.md`.

In preparation for release bump the version numbers of `types`,
`client`, and `node` to `0.6.0`.

Add changelog entries to each and update the lock files.